An updated review of the post-glacial history, ecology, and diversity of Arctic char (Salvelinus alpinus) and Dolly Varden (S. malma)

Arctic char (Salvelinus alpinus) and Dolly Varden (S. malma) are two closely related species in the genus Salvelinus. Both species show substantial intra-specific variation in ecology, morphology, and post-glacial history across their distributional ranges, which has presented substantial challenges for conservation and management and has led to the coining of the term, ‘the charr problem’. Arctic char and Dolly Varden have been studied extensively by scientists since the 1700s, not only because these fishes play important ecological roles within ecosystems, but also because they are culturally, economically, and recreationally valuable. While several detailed reviews have been published on Arctic char over the past 40 years, Dolly Varden remain understudied. In addition, advances in the fields of genetics, ecology, and morphometrics have improved our understanding of the behavior, feeding, habitat requirements, post-glacial histories and intraspecific diversity of each of these two species. Herein, we present an updated review that focuses on placing findings from more recently published (through 2022) phylogenetic, ecological and morphometric studies within the foundational context of earlier papers and reviews (since 1943). We also review anticipated effects of climate change on both species. Across their ranges, Arctic char and Dolly Varden can display a variety of life history types, with many populations exhibiting anadromy and/or potadromy; due to their use of distinct habitats at specific life stages, migratory chars are vulnerable to climate-induced changes to habitat quantity and quality. In addition to reviewing the existing literature, we highlight knowledge gaps and research priorities that, when addressed, will enable more informed conservation and management initiatives for these highly valued fishes.